The present invention relates to an image processing apparatus and method thereof, and more particularly, to an image processing apparatus and method thereof for performing conversion processing on image data by interpolation operation based on a conversion table, and a recording medium where data related to the image processing is recorded.
When image output is performed by a color printer or the like, color conversion is necessary. For instance, when R, G and B image data representing an image displayed on a computer monitor is outputted to a color ink-jet printer, the R, G and B image data need to be converted to C, M, Y and K signals for expressing ink colors used by the color ink-jet printer. As a color conversion method, matrix operation has conventionally been employed.
However, color conversion utilizing matrix operation has well-known disadvantages, such as insufficient color representation. For instance, when colors of an image displayed on a monitor are converted to colors of a printing image, color conversion characteristics must be precisely simulated. However, color conversion using matrix operation is far from satisfactory for such requirement.
In view of this, a lookup table interpolation method is available where a color conversion table is prepared in advance, and converted image data is obtained by interpolation operation based on the conversion table. For instance, Display and Imaging (SCI, Volume 2, Number 1, 1993, p17-25) discloses cubic interpolation using eight neighboring points, prism interpolation using six neighboring points, tetrahedron interpolation using four neighboring points and so on.
When such interpolation using a lookup table (LUT) is performed, there is a disadvantage in that the data size for a LUT becomes large. For instance, in the interpolation processing for outputting C, M, Y and K image data, assuming that a conversion table is divided into 16 grid points, wherein each color component data at each grid point has 8 bits, data having 4×17×17×17=19652 bytes are necessary.
Furthermore, in the case of a color ink-jet printer which realizes high precision image quality, seven colors of ink, including three c, m and y low density colors in addition to the conventional four colors (C, M, Y and K), are used. Therefore, the LUT data size for color conversion is further increased.